Oxygen-sensitive beverages and foods have a great economic importance worldwide. In particular beer, wine, fruit juices and tea-based beverages have to be mentioned. The packaging industry has developed a range of technologies in order to keep these filling materials unchanged in terms of taste and composition for as long as possible.
For example, in the case of bottles made of PET and similar plastics mono- or multi-layer composites have been used, which are intended to reduce the oxygen permeation. In these cases special polyamide or ethylene vinyl alcohol polymers (EVOH) are usual polymers. As an alternative having a passive barrier extremely thin coatings of carbon or silicon oxides can be applied in the bottle's interior. U.S. Pat. No. 8,377,530 B2 also describes the use of low molecular weight additives from the class of aromatic amides.
Glass bottles having a metal closure are preferably provided with barrier technologies, as described in EP-0503124 A1. Apart from this also oxygen-depleting compounds are used as described in EP 0328337 B1. Both technologies are used for sealants of crown corks, but have so far been limited to the use in so-called “pry-off” crown corks.
It is advantageous to use such compounds for seals of container closures which do not comprise PVC components, neither in the form of PVC nor in the form of plasticized PVC. In the conventional incineration of household waste acidic gases arise from halogen plastics whose escape into the atmosphere is harmful. In addition, even small amounts of PVC impede the mechanical recycling of plastic waste. Moreover, soft PVC-based sealing elements require the use of plasticizers, which are also of concern for health reasons.
There is therefore a demand for container closures which have a polymer based sealing insert, and preferably contain an oxygen-depleting component or oxygen-consuming component, which, however, are not based on PVC.
Hereinafter a polymer compound, or simply called a compound, as usual in the industry, is understood to be a blend of one or more polymers with other components (e.g., viscosity adjuster, extenders, fillers, pigments, antioxidants, lubricants) which are used to adjust the desired application properties. These application properties relate to the behavior of the compound from its preparation to the use in the production of container closures (e.g. when placing it in a closure blank to produce a sealing insert) as well as to the properties of the closure in filling and storage of the container and at its intended use (e.g. opening, removal of the beverage or foodstuff, re-closure of the container) by the consumer.
It is already known from WO 2011/069520 to employ a PVC-free polymer compound to which an oxygen-depleting component (also called a “scavenger”) has been added especially for twist crown caps. Preferably, these components are sulfite particles having a particular average particle size. By the sulfite a reduction of the oxygen ingress is achieved while the compound itself (that is, disregarding its scavenger content) need actually not have any certain barrier functions.
The compounds referred to in WO 2011/069520 are based on polypropylene and polyethylene, esp. LDPE and LLDPE, with contents of SEBS. SEBS has no useful barrier properties. These compounds contain substantial amounts of oil. In the embodiment white oil in an amount of 34% is the largest single component. The oil content is necessary in order to obtain the required physical parameters of the compounds.
For many applications, however, any oil content in a container sealing is undesirable. Oil can facilitate the migration of substances into and through the container sealing, which reduces the barrier properties of the seal. The resulting greater ingress of oxygen and other volatiles can affect the product properties.
In order to suppress such effects WO 2011/060803 proposed, for example, oil-free compounds especially when using fatty contents. However, barrier properties, optionally improved by scavenger substances, do not play a role.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.